Ordered Arrays of Be-Encapsulated Si Nanotubes on Si(111) Surface

Abstract

Using submonolayer Be deposition onto the Si(111) 7 × 7 surface under ultrahigh vacuum conditions, highly ordered honeycomb-like nanostructure arrays have been obtained. Scanning tunneling microscopy analysis of the nanostructure building blocks has revealed that they have composition, size, and properties similar to those theoretically predicted for the short Be-encapsulated Si nanotubes.Discovery of the carbon-based fullerenes, 1 nanotubes, 2 and cluster-assembled material, fullerite, 3 has inspired an extensive search of new candidate materials for nanostructure synthesis. Among other candidates, silicon is of especial interest due to the eminence of Si-based devices in the microelectronics industry. In the past decade, undoped and metal-encapsulated Si nanoclusters have been fabricated and characterized both by theory 4-8 and in experiments. 9-11 The promise for the formation of a cluster-based Si material has recently been demonstrated. 12 As for the Si nanotubes, they still remain the subject of merely theoretical consideration 13-17 which, in particular, predicts that metal (e.g., Be) encapsulation stabilizes Si nanotubes. 15 Following this hint, we have examined Be interaction with the heated Si(111) substrate under ultrahigh vacuum conditions and have detected the formation of Si-nanotube-related blocks arranged into ordered nanostructure arrays.The experiments were performed with an Omicron scanning tunneling microscope (STM) operated in an ultrahigh vacuum (∼1.0 × 10 -10 Torr). Atomically clean Si(111) 7 × 7 surfaces were prepared in situ by flashing to 1250°C after the samples were first outgassed at 600°C for several hours. Beryllium was deposited from a Ta foil tube. The Be deposition rate was estimated to be of ∼0.1 ML/min by counting the number of the Be-displaced Si adatoms in the Si(111) 7 × 7 surface at the very early stages of Be deposition. Vacuum during Be deposition was better than ∼1.5 × 10 -9 Torr. The samples were heated by passing DC current through them. For STM observations, electrochemically etched tungsten tips cleaned by in situ heating were employed. The STM images were acquired in a constantcurrent mode after cooling the sample to room temperature.When a submonolayer amount of Be is deposited onto the atomically clean Si(111) surface held at ∼500-650°C, formation of the ordered nanostructure arrays takes place as revealed using STM observations. As an example, Figure 1a shows an STM image of the 140 × 200 nm 2 surface area with two patches of nanostructure arrays located at the neighboring atomic terraces. The area around the patches is occupied by the original Si(111) 7 × 7 reconstruction from which some Si adatoms are displaced due to reaction with Be. The interior of the patches displays an ordered honeycomblike structure.Closer inspection of the high-resolution empty-state STM images clearly shows that the nanostructure array is arranged by stacking of hexagons of four different types, labeled A, B, C, and D in Figure 1b. The A-type hexagon is a regular hexagon with a side o...

Endohedrally Doped Cage Clusters

“…Despite the aforementioned theoretical predictions, only a few endohedrally doped 1D nanotubes have been synthesized in the laboratory. Following the predictions of Be doped silicon nanotubes, Saranin et al deposited Be atoms onto the Si(111) 7 × 7 surface under ultrahigh vacuum conditions and observed highly ordered honeycomb-like nanostructure arrays. Figure a shows the STM image of a 140 × 200 nm 2 surface area with two patches of nanostructure arrays, where the interior of the patches exhibits an ordered honeycomb-like structure.…”

Graphene-like bilayer hexagonal silicon polymorph

“…More interestingly, when confined to a quasione-dimensional (quasi-1D) nanopore (e.g., a carbon nanotube) both liquid silicon and water can freeze into single-walled polygonal nanotubes below their melting points [5,6]. The existence of single-walled polygonal ice nanotubes has been recently confirmed experimentally [7][8][9][10] and single-walled hexagonal silicon nanotubes containing a metal dopant have also been fabricated in the laboratory [11].…”

Synthesis of two-dimensional TlxBi1−x compounds and Archimedean encoding of their atomic structure

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